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Question: Answered & Verified by Expert
If from a wire of length 36 meter a rectangle of greatest area is made, then its two adjacent sides in meter are
MathematicsApplication of DerivativesJEE Main
Options:
  • A 6,12
  • B 9, 9
  • C 10, 8
  • D 13, 5
Solution:
2983 Upvotes Verified Answer
The correct answer is: 9, 9
$\begin{aligned} & \text { Given } 2(a+b)=36, \quad a+b=18 \\ & \text { Area of rectangle }=a b=a(18-a) \\ & A=18 a-a^2, \therefore \frac{d A}{d a}=18-2 a \\ & \text { Put } \frac{d A}{d a}=0 \text { i.e., } 18-2 a=0 \Rightarrow a=9 ; b=9\end{aligned}$

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